Problem: $-6fg - 3fh - 3f - 4 = -4g - 9$ Solve for $f$.
Combine constant terms on the right. $-6fg - 3fh - 3f - {4} = -4g - {9}$ $-6fg - 3fh - 3f = -4g - {5}$ Notice that all the terms on the left-hand side of the equation have $f$ in them. $-6{f}g - 3{f}h - 3{f} = -4g - 5$ Factor out the $f$ ${f} \cdot \left( -6g - 3h - 3 \right) = -4g - 5$ Isolate the $f$ $f \cdot \left( -{6g - 3h - 3} \right) = -4g - 5$ $f = \dfrac{ -4g - 5 }{ -{6g - 3h - 3} }$ We can simplify this by multiplying the top and bottom by $-1$. $f= \dfrac{4g + 5}{6g + 3h + 3}$